A promoter "cassette" plasmid will be constructed. Short, synthetic fragments of DNA containing either known PSs (Pribnow Sequences) or IRs (-35 promoter region) can be inserted into the plasmid and their in vivo and in vitro promoter efficiencies measured by a constant set of parameters. Comparison of promoter strengths (efficiencies) from synthetic promoters and hybrid arrangements of IR-PS will compare the contributions of these regions to overall promoter efficiency. This system will be used to investigate the spatial relationships of the IR-PS segments and the proposed secondary compensation site.